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247 

the brightness remaining on the north polar regions is not uniform, 
but is tinged with large dusky spaces, of a cloudy atmospheric ap- 
pearance. From which, and the fore-mentioned changes of colour 
at the polar regions, added to the changes he has formerly observed 
in the belts, we have, he thinks, sufficient reason to infer the exist- 
ence of a Saturnian atmosphere. 

The Bakerian Lecture, on some chemical Agencies of Electricity. By 
Humphry Davy, Esq. F.R.S. M.R.I.A. Read November 20, 1806. 
[Phil. Trans. 1807, .p. 1.] 

The chemical effects produced by electricity have, Mr. Davy says, 
long been objects of attention; but the novelty of the phenomena, 
their want of analogy to known facts, and the apparent discordance 
of some of the results, involved the inquiry in obscurity. 

It was very early observed, that acid and alkaline matter appeared 
in water acted upon by a current of electricity ; but Mr. Davy soon 
found that the muriatic acid came from the animal or vegetable mat- 
ters employed to connect the two portions of water ; for when the 
same cotton was repeatedly used, it ceased to be evolved. The soda, 
in like manner, was found to proceed from the corrosion of the glass 
tube, as it did not appear in water electrified in an agate cup. 

To be more certain of this effect, some distilled water was elec- 
trified in two agate cups, by the current from 150 four- inch plates, 
the communication between the cups being formed by moistened 
amianthus. In the first experiment soda was produced in the nega- 
tive cup, but the quantity was much less than when glass tubes were 
used; and on repeating the experiment, its quantity decreased, so 
that in the fourth experiment the presence of soda was scarcely per- 
ceptible in the residual water. The water in the other tube was sour, 
and appeared to contain nitrous acid, with excess of nitrous gas. As 
similar effects were produced by electrifying water in small gold 
cones, Mr. Davy suspected that some minute portion of saline matter 
had been carried over during the distillation of the water ; notwith- 
standing it did not affect nitrate of silver, or muriate of barytes. And 
on evaporating a quantity of it in a silver vessel by a heat not ex- 
ceeding 140° Fahrenheit, a small residuum was actually left, which 
appeared to be a mixture of nitrate of soda with nitrate of lead. A 
portion of this residuum being added to water electrified in the usual 
manner, and which had attained the maximum of its effect upon tur- 
meric paper, considerably increased those effects. 

Water slowly distilled, being electrified either in gold cones or 
agate cups, did not evolve any fixed alkaline matter, though it ex- 
hibited signs of ammonia ; but in tubes of wax, both soda and potash 
were evolved, and the acid matter in the positive cup was a mixture 
of sulphuric and muriatic acids. In a tube of resin the alkali was 
principally potash. In cups of Carrara marble, primitive marble from 
Donegal, argillaceous schist from Cornwall, serpentine from theLizard, 
and grauwacke from North Wales, soda was uniformly evolved. 



248 

This probably arose from a minute portion of common salt being 
contained in them, for the Carrara marble yielded a sensible quan- 
tity on analysis ; and on repeating the electrifying of the water in 
the cup formed of it, the presence of soda became less visible every 
time, and at length disappeared entirely ; but the production of lime- 
water was uniform. A bit of glass added to water, which was elec- 
trifying in the gold cones, caused it to exhibit almost immediately 
the presence of soda. 

In every instance nitrous acid was uniformly found in the positive 
cup, which appeared to proceed from the combination of nascent 
oxygen with the nitrogen of the common air absorbed by the water. 
The longer the operation was continued, the more acid was produced, 
arising from the air which continued to be absorbed. Volatile alkali 
was also constantly formed, from the combination of the nascent hy- 
drogen with the nitrogen ; but it soon attained its utmost limit, as 
hydrogen during its solution in water seems to expel nitrogen. When 
water was electrified in vacuo scarcely any nitrous acid, and no vo- 
latile alkali, was formed. When electrified in a receiver filled with 
hydrogen (the common air originally contained in the water having 
been extracted by the air pump), neither nitrous acid nor volatile al- 
kali was found in the water. 

In all these processes, the acid matter collected in the water round 
the point transmitting the electricity, and the alkaline matter round 
that which received it. When water was even electrified in two cups 
made of sulphate of lime, it was found that the water connected with 
the positive wire contained sulphuric acid, while that in the other 
cup was a pure and saturated solution of lime. Similar effects were 
produced when use was made of cups of sulphate of strontian, fluate 
of lime, or sulphate of barytes. It also appeared, that very minute 
portions of acid or alkaline matter might be disengaged by this 
means from solid combinations, consisting principally of the pure 
earths. When cups were used made of a basalt which contained 
3^ parts of soda, and nearly half a part of muriatic acid, with fifteen 
parts of lime in the 100, oxymuriatic acid was found in the positive 
cup, and a mixture of lime and soda in the other. A cup of compact 
zeolite, containing seven per cent, of soda, yielded soda and lime to 
the water connected with the negative wire. Lepidolite yielded 
potash, and vitreous lava from Etna yielded a mixture of soda, pot- 
ash, and lime. 

Mr. Davy attempted to ascertain whether the weight of the alkali 
obtained, agreed with the weight lost by the substance operated upon. 
Water was electrified negatively for four days, by a current from 150 
plates, in a glass tube that weighed 84.VV grains. The positive wire 
was inserted into water, contained in an agate cup, and the commu- 
nication was kept up by moistened amianthus. At the end of the 
process the glass tube weighed 84 ,y T grains. The water being eva- 
porated, yielded T V ff grains of a mixture of soda, with a white powder 
insoluble in acids. 

When soluble compounds were put into water, contained in agate 



249 

cups, and electrified, the decomposition was more rapid. A solution 
of sulphate of potash being put into each of the cups, and electrified 
by means of fifty pair of plates for four hours, the acid was found by 
itself in the positive cup, and the alkaline bases in the negative cup. 
Similar phenomena took place with sulphate of soda, nitrate of pot- 
ash, nitrate of barytes, sulphate of ammonia, and alum. When mu- 
riatic salts were used, these yielded oxymuriatic acid. When com- 
patible mixtures of neutro-saline compounds were used, the different 
acids and bases separated in a mixed state, without any regard to 
their affinities. When solutions of metals, deoxidizable by nascent 
hydrogen were employed, metallic crystals formed on the negative 
wire, and some oxide was deposited ; but solutions of iron, zinc, and 
tin, only deposited oxide ; a great excess of acid was soon observed 
on the positive side. Although stronger solutions afforded signs of 
decomposition quicker than weaker ones, yet even the smallest pro- 
portions seemed to be acted upon with equal energy : as paper tinged 
with turmeric was immediately rendered brown when plunged into 
pure water and brought into contact with the negative point ; so 
paper tinged with litmus was immediately reddened by the positive 
point, in consequence of the very minute portion of saline matter 
contained in the paper ; and it further appeared, that in all these 
decompositions the separation of the constituent parts from the last 
portions of the compounds was complete when the operation was 
sufficiently protracted. 

The contact of the solution with the wires was not necessary for 
its decomposition ; for muriate of potash being put into the middle 
tube of a series of three, the outer ones containing only water and 
the wires, alkali soon appeared in that connected with the negative 
wire, and acid in the other ; and at length they were obtained per- 
fectly separate. 

In thus causing the acids to be thus transferred from a saline com- 
pound into water, through moistened amianthus, no change was ob- 
served to take place in litmus paper placed near the amianthus. The 
reddening of the litmus paper always took place just above the posi- 
tive point, and then slowly diffused itself to the middle of the vessel. 
Similar effects were observed when the alkali was transferred, the 
turmeric paper first becoming brown close to the negative wire. 

When three glass tubes were used, the two outer tubes holding a 
solution of muriate of soda, and the middle one sulphate of silver, a 
communication being made with the central vessel by turmeric paper 
on the positive side, and by litmus paper on the negative, neither of 
the papers had its colour changed, although the muriatic acid passing 
through the amianthus occasioned a dense heavy precipitate in the 
sulphate of silver, and the soda a more diffuse and lighter one. 

Acid or alkaline substances will also pass through liquids, having 
a strong attraction for them. In an apparatus of three tubes, Mr. 
Davy found that sulphuric acid, evolved from sulphate of potash, 
would pass into water, through either ammonia, lime-water, or weak 
solutions of potash or of soda. The only effect of strong solutions of 



250 

potash or soda was to increase the time necessary for this transfer. 
Muriatic or nitric acids were also transmitted through alkaline solu- 
tions ; and, vice versd, alkaline matter, hy changing the arrangement 
of the liquids, was transmissible through the acids : even magnesia 
was transferred like the other bases. But when it was attempted to 
pass sulphuric acid through aqueous solutions of barytes or of stron- 
tian, on the contrary, the sulphate of those earths was deposited in 
the intermediate tube. 

Muriate of barytes being positive, sulphate of potash intermediate, 
and water negative, potash appeared in the water, and sulphate of 
barytes was deposited in the intermediate vessel. 
■ Muriate of barytes being negative, sulphate of silver intermediate, 
and water positive, sulphuric acid only appeared in the water, and 
muriate of silver was deposited in the intermediate vessel. 

Mr. Davy then proceeds to develop the theory of these pheno- 
mena : and he first considers the mode of decomposition and transi- 
tion. Hydrogen, alkaline substances, and metallic oxides, are at- 
tracted by negatively electrified metallic substances, and repelled by 
positive ones : contrary effects take place with oxygen and the acids. 
He thinks these electric energies are communicated from one particle 
to another of the same kind, so as to establish a conducting chain in 
the fluid, as acid matter is always found in the alkaline solutions 
through which it is transferred, as long as any acid matter remains 
at the original source. It is possible that there may be, in some 
cases, a succession of decompositions and recompositions ; but the 
process is not absolutely necessary, as pure acids and alkalies pass 
through water to the points by which they are attracted. It appears 
that this power of transference is overcome by gravity in attempting 
to pass barytes through sulphuric acid, or muriatic acid through sul- 
phate of silver. To these instances he adds, that magnesia and the 
metallic oxides will not pass through an intermediate vessel of water, 
but sink to the bottom. 

In the decomposition of water, a particle of oxygen is attracted by 
the positive point, and at the same time a particle of hydrogen is re- 
pelled by it; the opposite process takes place at the negative point: 
and. in the middle of the circuit there must be a new combination of 
the repelled matter, in the same manner as when two portions of 
muriate of soda are separated by water ; muriatic is repelled from 
the negative side, and soda from the positive side ; so that muriate 
of soda is composed in the middle vessel. 

Although similar effects could not be produced by silently passing 
a strong current of electricity from an electrical machine for four 
hours, through sulphate of potash, yet they were produced by using 
platina wires yVth of an inch in diameter, cemented in glass tubes ; 
so that no doubt can arise but that the principle of action is the same 
in common as in voltaic electricity. 

It was known that many bodies brought into contact and then se- 
parated, exhibited opposite states of electricity ; and Mr. Davy him- 
self had observed, that when acid and alkaline solutions were em- 



251 

ployed in alternation with plates of a single metal, the alkaline solu- 
tion received the electricity from the metal, and the acid transmitted 
it to the metal. So in the simplest case of electrical action, the alkali, 
receiving electricity from the metal, would, on being separated from 
it, appear positive, and of course be repelled by positively electrified 
surfaces, and attracted by negatively electrified surfaces ; the acid, 
acquiring the contrary electricity, following the contrary order. 

Several phenomena accord with this idea. Sulphur separated from 
its contact with a metal is positive; and, in like manner, sulphur 
separated from sulphuric acid by electricity is attracted by the nega- 
tive surface. And again, hydrogenated sulphuretted alkalies, being 
composed of three substances, all positive, are so very active in vol- 
taic combinations as, in certain cases, to overpower the energies of 
the metals. 

Mr. Davy then considers the relation between the electrical energy 
of bodies and their chemical affinities ; and observes, that all the sub- 
stances that combine chemically, exhibit, so far as is known, opposite 
electric states ; and that, in the various experiments of decomposition 
by electricity, the natural electrical energies of the constituent parts 
of the compounds acted on are, as it were, overpowered by the arti- 
ficial electricities : so that it is probable that chemical affinity depends 
upon the different electrical energies of the acting bodies. 

And upon this supposition, particles possessed of opposite electrical 
states and freedom of motion will enter into combination. When two 
bodies possessed of the same state act upon a third body possessed of 
the opposite state, the substance possessing the weakest energy will 
be repelled. In other cases there maybe such a balance of attractive 
and repellent powers as to produce triple compounds, or even more 
complicated combinations. It will also be easy to explain the in- 
fluence of the masses of bodies upon their affinities ; for the combined 
effect of many particles possessing a feeble electrical energy may be 
conceived equal, or even superior, to the effect of a few particles 
possessing a strong electrical energy ; and, accordingly, we find that 
concentrated alkalies resist the transmission of acids more powerfully 
than weak ones. 

As the strength of the electricity diminishes from the points to the 
middle of the water, a measure of the artificial energies may be ob- 
tained by the place where the compounds begin to be decomposed. 
Thus sulphate of barytes requires intermediate contact with the 
wires ; and when 150 pieces of plates were used with a circuit of 
water often inches, sulphate of potash was not decomposed at four 
inches from the positive wire ; but when brought within two inches, 
its alkali was strongly repelled. 

As heat and light are the consequences of a restoration of the equi- 
librium between bodies in a high state of opposite electricities, so are 
they also the result of all intense chemical action; and again, as when 
large quantities of electricity of low intensity act, heat is produced 
without light, so in low combinations the temperature only is in- 
creased. The effect of heat in promoting chemical action seems not 



252 

confined to the freedom of motion it gives to the particles, but to the 
exaltation of the electrical energies of bodies, such as is well known 
to take place in glass, tourmalin, and sulphur. The electricity of an 
insulated plate of copper, and a plate of sulphur, was scarcely sen- 
sible at 56° Fahr. to the condensing electrometer; at 100° they 
affected the gold leaves without condensation ; they increased in a 
still higher ratio as the sulphur approached its melting point ; and at 
a little above that point, the two substances rapidly combine, and 
evolve heat and light. In general, when the different electrical ener- 
gies are equally strong, the combination seems to be vivid, the heat 
and light intense, and the new compound is in a neutral state, as in 
combustion, and the union of the strong acids with the alkalies ; but 
when only the energy is strong, the effect is less vivid, and the com- 
pound exhibits the excess of the stronger energy. 

Mr. Davy then considers the theory of the Voltaic apparatus ; and 
remarks, that the above facts seem to reconcile Volta's own theory 
with the chemical theory of galvanism. 

In a pile of zinc, copper, and water, the plates are in opposite 
states of electricity ; and in regard to such low electricity, the water 
is an insulating body. Of course, each plate produces an opposite 
electricity upon the opposite plate, the intensity increasing with the 
number, and the quantity with the extent of the series. Upon con- 
necting the extreme points, the opposite electricities tend to produce 
an equilibrium, which would cause the motion to cease : but the 
fluid medium being composed of two elements possessing opposite 
electrical energies, the oxygen is attracted by the zinc, and the hy- 
drogen by the copper. Hence the balance of power is only momen- 
tary ; for oxide of zinc is formed, and hydrogen is disengaged. The 
electricity acquired by the copper is communicated anew to the zinc, 
and the process continues as long as the chemical changes are carried 
on. 

Neither the conducting nor solvent powers of the fluid mediums 
are a principal cause of their activity ; for strong sulphuric acid has 
very little activity in the pile. The effect of neutro-saline solutions 
diminishes when troughs are used, according as their acid arranges 
itself on the side of the zinc plates, and their alkali on the other ; 
but the energy may be restored by agitating the fluids in the 
cells. 

As sensible heat appears when an equilibrium is produced by small 
metallic surfaces in the voltaic battery, the opposite states being 
exalted, so if the decomposition of the chemical agents be essential 
to the balance of the opposed electricities, the decomposition of the 
saline solutions ought to be attended with an increase of temperature. 
To water electrified in the gold cones by the power of 100 plates, a 
drop of solution of potash was added in the positive cone : potash 
immediately passed over, and in less than two minutes the water was 
in a state of ebullition. When solution of nitrate of ammonia was 
employed, the water was evaporated in three or four minutes with a 
kind of explosive noise, and inflammation took place. The pure alka- 



253 

lies, or acids, produced very little effect, although they are better con- 
ductors. 

Lastly, some general applications of these singular facts are pointed 
out by Mr. Davy ; such, for instance, as the application of electricity 
to the analysis of animal and vegetable substances. Muscular fibre 
being electrified for some time, became dry and hard ; and it left, 
upon incineration, no saline matter. Potash, soda, ammonia, lime, 
and oxide of iron, were collected on the negative side ; and the sul- 
phuric, nitric, muriatic, phosphoric, and acetous acids, on the posi- 
tive. Laurel-leaf was rendered brown and parched ; green colouring 
matter, with resin, alkali, and lime, appeared in the negative vessel, 
and prussic acid in the positive. 

By using charcoal and plumbago, or charcoal and iron, as the ex- 
citing powers, along with neutro-saline solutions, large quantities of 
acids and alkalies might be procured with little trouble or expense. 

It is very probable that many mineral formations have been mate- 
rially influenced or even occasioned by the agency of the electricity ; 
and the electrical power of transference may thus be applied to the 
explanation of the principal points in geology. 

On the Precession of the Equinoxes. By the Rev. Abram Robertson, 
M.A. F.R.S. Savilian Professor of Geometry in the University of 
Oxford. Read December 18, 1806. [PM. Trans. 1807,^. 57.] 

The Professor observes, that Sir Isaac Newton was the first ma- 
thematician who endeavoured to estimate the quantity of the pre- 
cession from the attractive influence of the sun and moon on the 
spheroidal figure of the earth. His investigations relating to this 
subject evince the same transcendent abilities that are displayed in 
other parts of his Principia ; but it is admitted, that, from a mistake 
in his process, his conclusion is erroneous. 

The investigations of other mathematicians in attempting the solu- 
tion of the same problem are arranged by the author under three 
general heads. The first arrive at wrong conclusions, in consequence 
of mistake in some part of their proceedings ; the second obtain just 
conclusions, but rendered so by balance of opposite errors ; the third 
approach as near the truth as the nature of the subject will admit, 
but, in the author's estimation, are liable to the charge of obscurity 
and perplexity. 

The defects in all their investigations Professor Robertson ascribes 
to the same cause — the uncultivated state of the doctrine of com- 
pound rotatory motion. 

The author's endeavours are, consequently, first directed to the 
investigation of the principles of compound rotatory motion from 
principles which he considers clear and unexceptionable. 

He next proceeds to calculate the disturbing solar force on the 
spheroidal figure of the earth, and thence the angular velocity which 
it produces. 

The quantity of annual precession is then computed ; and, lastly,